1) Field of the Invention
The invention relates to a device for determining the position of a body to be positioned relative to a reference point.
2) Description of Related Art
Position determining devices serve, for example, for controlling measurement and production machinery, and for determining paths between longitudinally shiftable objects such as measurement heads, handles or mounting arms. For these applications the precision with which these paths can be determined is of prime importance for the manufacturing precision of the automatic machinery.
A method and a device which makes a high degree of measurement precision possible independently from an exact conduction of a sampler are already known from DE-OS 39 09 856. For this, three marks of a graduated scale are evaluated by a sampler. For two marks, the projection angle formed between a projection center and these marks is independent from the distance the projection center is located above the marks and how far the projection center is laterally displaced. For three marks, the projection center is exactly determined via the additional projection angle between the projection center, this additional mark and one of the other marks. For a combination of two combination angles, there exists only one location at which the projection center can be situated.
So that the marks on this graduated scale can be reproduced on a projection surface of the sampler, the graduated scale must be evenly lit. This could occur through vertical illumination or back lighting. However, a lighting device requires additional space which stands in opposition to aspirations of miniaturization.